计算几何？学了不会？会了不对？ 

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 const double EPS=1e-6;
 4 inline int dcmp(double x){
 5     if(fabs(x)<EPS)return 0;
 6     else if(x<0)return -1;
 7     else return 1;
 8 }
 9 #define Point Vector 
10 struct Vector{
11     double x,y;
12     Vector(double X=0.0,double Y=0.0):x(X),y(Y){}
13     Vector operator+(const Vector &A)const{
14         return Vector(x+A.x,y+A.y);
15     }
16     Vector operator-(const Vector &A)const{
17         return Vector(x-A.x,y-A.y);
18     }
19     double operator*(const Vector &A)const{//点乘· 
20         return x*A.x+y*A.y;
21     }
22     Vector operator*(const double &X)const{//数乘 
23         return Vector(x*X,y*X);
24     }
25     bool operator==(const Vector&A)const{
26          return ( !dcmp(x-A.x) && !dcmp(y-A.y) );
27     }
28     bool operator<(const Point &A)const{
29         return dcmp(x-A.x) ? x<A.x : y<A.y ;
30     }
31 };
32 inline double polarangle(Vector &A){//向量极角
33     return atan2(A.y,A.x); //?什么函数? 
34 }
35 inline double cross(const Vector &A,const Vector &B){//叉乘* （只取数值大小） Arg(A)<Arg(B)时取正值 
36     return A.x*B.y-A.y*B.x;
37 }
38 inline double length(const Vector &A){
39     return sqrt(A.x*A.x+A.y*A.y);
40 }
41 inline Point meet(const Point &P1,const Vector &u,const Point &P2,const Vector &v){
42     return P1+u*(cross(P1-P2,v)/cross(v,u));
43 }
44 inline double dis(const Point &A,const Point &P,const Vector &u){
45     return fabs(cross(A-P,u)/length(u));
46 }
47 /*inline double dis(const Point &A,const Point &P,const Point &Q){
48     return fabs(cross(A-P,Q-P)/length(Q-P));
49 }*/
50 const int maxn=1e5+5;
51 Point p[maxn],sta[maxn];
52 int n,k;
53 
54 inline void Andrew(){
55     sort(p+1,p+n+1);
56     sta[0]=sta[k=1]=p[1];//放1 or 放2? 
57     for(int i=2;i<=n;i++){
58         if(p[i]==p[i-1])continue;//去重 
59         while(cross(p[i]-sta[k],sta[k]-sta[k-1])<0)k--;
60         sta[++k]=p[i];
61     }
62     for(int i=n-1;i;i--){//必须循环到1：保证下凸包的正确性 
63         if(p[i]==p[i+1])continue;//去重 
64         while(cross(p[i]-sta[k],sta[k]-sta[k-1])<0)k--;//凸包边上无点：<= 
65         sta[++k]=p[i];
66     }
67 }
68 int main(){
69     scanf("%d",&n);
70     for(int i=1;i<=n;i++){
71         scanf("%lf %lf",&p[i].x,&p[i].y);
72     }
73     Andrew();
74     double ans=0.0;
75     for(int i=1;i<k;i++)ans+=length(sta[i+1]-sta[i]);
76     printf("%.2lf",ans);
77     return 0;
78 }
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posted @ 2020-05-15 22:11  Tj1  阅读(102)  评论(0)    收藏  举报